If you're thinking about leading a more active lifestyle, you're not alone. In recent years, an increasing number of Americans have started participating in more sports, fitness, and recreation. Whether you're trying to get fit or build muscle, or you're just tired of the couch, here are some changes you can expect along the way.

What happens to your body when you start exercising regularly?

During that first workout, you might feel more alert and energized because ramping up your heart rate means a boost in overall blood flow and oxygen to the brain. But prepare yourself for the day after, when you'll almost certainly get a case of DOMS, short for delayed onset muscle soreness. The soreness will persist for about 72 hours, but the good news is you're less likely to get it again as long as you continue to regularly exercise those same muscles.

Over the next few weeks, you'll slowly start to ramp up production of mitochondria via a process called mitochondrial biogenesis. Mitochondria are the parts of your cells that convert carbs, fat, and protein into fuel that your muscles use to do their job, like flex and contract. After six to eight weeks, studies have shown that people can increase their mitochondria by up to 50%. With more mitochondria in your cells, you'll start to feel more fit, and your endurance will increase. So running three miles will no longer feel as difficult as it did during that first week.

Once you're six months in, all that hard work should finally start to show. If your workouts focus on strength training, you'll notice your muscles begin to take shape. You're also less likely to fall off the workout wagon at this point. Exercise programs often see a 50% dropout rate within the first six months, but after that more people stick with it.

Now, if you're more focused on cardio, then by nine months of regular exercise you should see about a 25% increase in your VO2 max. VO2 max is often used as a measure of fitness and refers to the rate your body can transport oxygen to your muscles for fuel. Basically, higher VO2 max means you can run faster for longer. So a 25% increase in VO2 max, for example, means you can run about 20% farther in the same amount of time.

After one year of regular exercise, your bones will be denser, which reduces your risk of osteoporosis. In fact, researchers have found that regular resistance training, when combined with aerobic exercise, can actually reverse the effects of osteoporosis after 12 months.

Now, if you maintain your exercise program long term, your body might not be the only thing to benefit. Your bank account may also beef up a bit. One study revealed that older people who exercised five days a week for at least 30 minutes saved, on average, $2,500 a year in medical costs for heart-related health problems alone. You'll also be at a lower risk of developing arthritis, type 2 diabetes, dementia, and certain types of cancer like breast and colon.

In all probability, you're going to live longer than you otherwise would. And that longer life, it will likely feel more fulfilling, because exercise lowers the risk of anxiety and depression by reducing levels of stress hormones, like cortisol and adrenaline.

Of course, all these benefits depend on the type and intensity of your workout and how long you exercise for each week. A balanced diet is also paramount to a healthy lifestyle. For the average adult ages 18 to 64, the US Department of Health and Human Services recommends either a minimum of 2 1/2 hours per week of moderately intense exercise, like brisk walking or biking. Or at least 1 hour and 15 minutes each week that combines moderate and high-intensity workouts, like running or swimming sprints.

On top of that, make sure and take two days each week to strengthen your muscles with some weights or resistance training. This will help your overall speed and endurance. As you begin, it's important to pace yourself and not push too hard too fast, or you risk serious injury.

You'll discover that the fitter you become, the easier it will be to exert a little more energy the next week, the week after, and so forth.